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Abstract

It has recently been shown that spatial light interference microscopy (SLIM) developed in our laboratory can be used to quantify the dry mass growth of single cells with femtogram sensitivity [M. Mir et al., Proc. Nat. Acad. Sci. 108, 32 (2011)]. Here we show that it is possible to measure the motility of single cells in conjunction with the dry mass measurements. Specifically the effect of poly-L-lysine substrate on the dry mass growth of Drosophila S2 cells is studied. By measuring the mean square displacement of single cells and clusters it is shown that cells that adhere better to the surface are unable to grow. Using such a technique it is possible to measure both growth and morphogenesis, two of the cornerstones of developmental biology.

Figures (3)

a) Trajectories of attached (red line) and motile (black line) cells. Time-stamped insets show the tracked cell at various time points. It can be seen that the motile cell exhibits a clear directional motion over time whereas the adherent cell is jostling in place. b) The dry mass growth of the two cells shown in a, the attached cell exhibits no growth whereas the motile cell approximately doubles its mass. c) MSD for the two cells shown in b.

a) Semilogarithmic plot MSD vs. time for all the individual cells tracked. It can be seen that the MSD increases by 3-4 orders of magnitude between the 1st and 4th generations b) Semilogarithmic plot of the maximum MSD vs. the approximated linear growth rate for each cell.

Dry mass vs. time for cell clusters in the 3rd and 4th generations. Each colored time series corresponds to a single cluster, the solid black line is the average exponential fit for each cluster, with the average time constant, τ shown for each fit.